Welcome to PhantomPilots.com

Sign up for a weekly email of the latest drone news & information

Winglet - good for planes, good for props?

Discussion in 'General Discussion' started by isky172, Aug 31, 2014.

  1. isky172

    Joined:
    Jul 9, 2014
    Messages:
    78
    Likes Received:
    1
    A prop is nothing more than a rotating wing. Winglets are used to increase efficiencies of various flight characteristics. Anyone see a reason why we can't get winglets as a propeller option for multi-rotor aircraft?
     

    Attached Files:

  2. slothead

    Joined:
    Jun 14, 2014
    Messages:
    485
    Likes Received:
    2
    Location:
    Frederick, MD, USA
    My only hesitation would be that they could offer drag when vectoring normal to the axis of the winglet. Aircraft always fly with the winglet cutting through the air while the copter would be spending a good bit of time moving against the winglet, also, you don't see winglets on the end of full-scale props (as far as I know). Just my $0.02
     
  3. SJBrit

    Joined:
    Feb 10, 2014
    Messages:
    115
    Likes Received:
    0
    Location:
    Huntsville, AL
    I'm not sure it would help. You'll notice that winglets are only seen on swept-back wings. The reason is that when a wing is swept back there is a tendency for the airflow to be partially along the wing towards the tip. That flow reduces the flow normal to the wing and therefore decreases efficiency. The winglet is there to eliminate that airflow along the wings (by blocking it) and therefore getting all the efficiency back with 100% normal flow.

    Forward motion notwithstanding (it's largely irrelevant compared to rotational speed) a prop is equivalent to a wing which is normal to the fuselage - no sweep back. So for this wing, and for props, the airflow is always normal to to airfoil: there's no airfoil angle to promote flow towards the tip. So, the way I see it, a winglet on a prop would't do anything since it's the solution to a problem that doesn't occur with props.
     
  4. isky172

    Joined:
    Jul 9, 2014
    Messages:
    78
    Likes Received:
    1
    As long as it doesn't hurt other aspects of flight, I think it could increase forgiveness at the VRS envelope. Removing (or at least, significantly reducing) the creation of wing vortices is a primary function of those widgets. I wouldn't think they would have to be big either - something just a few millimeters in height from the top of the prop tip, sweeping back away from the leading edge by just a few degrees to a width 1/2 to 1/3 the width of the prop tip.
     
  5. ProfessorStein

    Joined:
    Jun 20, 2014
    Messages:
    1,136
    Likes Received:
    3
    Location:
    Portland, OR
    They are appearing on the props of the big wind turbines. But, yeah, those are pretty stationary, aren't they (one would hope).

    If I remember right, there were bent-tip props on some navy fighters on the carriers during the war, but I'm not finding any photos.

    But for a copter, I would think winglets would interfere with the craft's ability to move laterally, because the prop won't want to "slide".
     
  6. locoworks

    Joined:
    Jul 4, 2014
    Messages:
    471
    Likes Received:
    10

    i agree with you, but some wind turbines have winglets on the blades so they must do something for props??? but maybe only on really big props that don't deal with wind side on like a quad prop does in lateral flight??
     
  7. Monte55

    Joined:
    Apr 26, 2014
    Messages:
    2,198
    Likes Received:
    517
    Location:
    Raymore Missouri
    I would think centripetal force on those would be hell to deal with on a rotor.
     
  8. HeliRy

    Joined:
    Jan 9, 2014
    Messages:
    121
    Likes Received:
    0
    Location:
    Vancouver Island, Canada.
    Very true. Plus that much force on the tip of a blade would cause a catastrophic failure of the entire thing within seconds. Either the winglet would snap off, or the blade would snap somewhere in the middle.

    It would be cool if we could get away with it, but there are many reason why modern helicopters and propellers don't employ these.
     
  9. SJBrit

    Joined:
    Feb 10, 2014
    Messages:
    115
    Likes Received:
    0
    Location:
    Huntsville, AL
    Interesting. I've just been reading up on winglets for wind turbines. The question I suppose is whether the advantages outweigh the disadvantages on small, high RPM props. The winglets in the turbines reduce friction due to tip vortices, but then they add friction (drag) of their own. They also add mass a LONG way from the axis so that's a big increase in moment of inertia - that will increase the current demand on the rest of the drive.
     
  10. ProfessorStein

    Joined:
    Jun 20, 2014
    Messages:
    1,136
    Likes Received:
    3
    Location:
    Portland, OR
    I assume you mean centrifugal rather than centripetal. Centrifugal would be the forces trying to rip the winglet away. Centripetal would be the forces that keep it from ripping away.

    But there are examples of props with bent tips, even before the era of carbon fibre... so I'm guessing the centrifugal forces are not as insurmountable as one might think.

    [​IMG]


    Bent tips on rotary wings, while certainly not prevalent, do exist... particularly on larger machines.

    [​IMG]

    But from what I hear, Sikorsky put bent tips on the S-92 (above) to aid mostly in hovering. Once the craft induces lateral movement, the advantage of the tips goes away, and they may actually lead to increased drag.
     
  11. Monte55

    Joined:
    Apr 26, 2014
    Messages:
    2,198
    Likes Received:
    517
    Location:
    Raymore Missouri
    My bad. You're correct. I was using a spell check and didn't pay close attention. Thanks.
     
  12. SJBrit

    Joined:
    Feb 10, 2014
    Messages:
    115
    Likes Received:
    0
    Location:
    Huntsville, AL
    Just for the record, there is no such thing as centrifugal force in a physical sense. The centripetal force is the force required to keep an object spinning in a circle and is directed along the radius towards the center of the circle. No force pulls the object in the opposite direction. So, in a prop centripetal force manifests as tension in the structure pulling the physical structure towards the center.

    Sorry - couldn't help myself :)
     
  13. ProfessorStein

    Joined:
    Jun 20, 2014
    Messages:
    1,136
    Likes Received:
    3
    Location:
    Portland, OR
    While the force is Fictitious, it is how we describe what is happening... why the prop wants to tear itself apart at the hub... and definitely can be calculated.
    http://www.calctool.org/CALC/phys/newtonian/centrifugal

    There are a number of Fictitious forces in Newtonian Law. But they are "made up" for the very reason to describe the indescribable and "apparent" (to provide the counterpoint to existing forces - and preserve Newton's Third Law). To say there's "no such thing as centrifugal force" is incorrect. It has been defined, and is what we would use to describe the action in this case. It's like saying there's no such thing as Tex Mex, so you can't order it from the menu.
     
  14. SJBrit

    Joined:
    Feb 10, 2014
    Messages:
    115
    Likes Received:
    0
    Location:
    Huntsville, AL
    Well, I'll grant you that in the frame of reference of a rotating object there is indeed a centrifugal force that is useful to think about for calculation purposes. But I did choose my words carefully: there is no centrifugal force in a physical sense. The only physical force acting on a rotating object (assuming no drag) is one towards the center of the circle. In a prop that is supplied by tension in the structure which is why it wants to pull itself apart.